Occasionally defied a religious festival (3)
I believe the answer is:
eid
'religious festival' is the definition.
(I've seen this before)
'occasionally defied a' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'defied'+'a'='defieda'
The alternate letters of 'defieda' are 'EID'.
(Other definitions for eid that I've seen before include "feast" , "religious festival" .)